Observations of radio waves in the Earth's plasma environment, characterized by a discrete rather than continuous frequency pattern, are described with theoretical discrete eigenmodes trapped within a plasma with density structuring. Originally applied for modeling or auroral radio waves (auroral roar), the theory is here extended to describe auroral kilometric radiation (AKR), characterized by fine frequency structure, kilometric continuum radiation, and other in-situ observations of discrete radio emissions at F-region altitudes. This research stresses investigation of AKR fine-structure, described as electrostatic eigenmodes that mode-converted to electromagnetic waves, that can be detected at a distance from the source.
